[FLINK-33392][docs] Add the documentation pages for balanced tasks scheduling.

[RocMarshal]

What is the purpose of the change

[FLINK-33392][docs] Add the documentation pages for balanced tasks scheduling.

Brief change log

[FLINK-33392][docs] Add the documentation pages for balanced tasks scheduling.

Verifying this change

N.A

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 84ff482 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[RocMarshal]

The CH edition page will added a copy in the corresponding location after the EN edition page is ready.

[ruanhang1993]

@davidradl Please help to review this PR agian. @RocMarshal please remember to pick this to release-2.2 branch.